In one well-known type of gas turbine engine (GTE), at least one high pressure turbine (HPT) nozzle is mounted within an engine casing between a combustor and a high pressure (HP) air turbine. In single nozzle GTE platforms, the HPT nozzle typically includes an annular nozzle flowbody having an inner nozzle endwall and an outer nozzle endwall, which circumscribes the inner nozzle endwall. A plurality of circumferentially spaced stator vanes extends between the outer and inner nozzle endwalls and cooperates therewith to define a number of flow passages through the nozzle flowbody. The HPT nozzle further includes one or more radial mounting flanges, which extend radially outward from the HPT nozzle flowbody. The radial mounting flanges are each rigidly joined to a different end portion of the nozzle flowbody and may be integrally formed therewith as a unitary machined piece. When the GTE is assembled, the radial mounting flanges are each attached (e.g., bolted) to corresponding GTE-nozzle mounting interfaces (e.g., inner walls) provided within the GTE to secure the HPT nozzle within the engine casing.
During GTE operation, the HPT nozzle conducts combustive gas flow from the combustor into the HP air turbine. The combustive gas flow convectively heats the inner surfaces of the combustor and the HPT nozzle flowbody to highly elevated temperatures. At the same time, the HPT nozzle's radial mounting flanges and the GTE-nozzle mounting interfaces are cooled by bypass air flowing over and around the combustor. Significant temperature gradients thus occur within the GTE during operation, which result in relative thermal movement (also referred to as “thermal distortion”) between the HPT nozzle, the GTE-nozzle mounting interfaces, and the trailing end of the combustor. Due to their inherent rigidity, conventional HPT nozzles of the type described above are often unable to adequately accommodate such thermal distortion and, as a result, can experience relatively rapid thermomechanical fatigue and reduced operational lifespan. In addition, thermal distortion between the HPT nozzle, the combustor end, and the GTE-nozzle mounting interfaces can result in the formation of leakage paths, even if such mating components fit closely in a non-distorted, pre-combustion state. Compression seals may be disposed between the nozzle mounting flanges and the GTE-nozzle mounting interfaces to minimize the formation of leakage paths. However, the sealing characteristics of the compression seals can be compromised when the nozzle mounting flanges, and specifically when the mounting flange sealing surfaces contacting the compression seals, are heated to elevated temperatures by combustive gas flow through the turbine nozzle flowbody. Although the radial height of the mounting flanges can be increased to further thermally isolate the flange sealing surfaces from the combustive gas flow, increasing the height of the radial mounting flanges undesirably increases the overall envelope of the HPT nozzle and consumes a greater volume of the limited space available within the engine casing.
There thus exists an ongoing need to provide a turbine nozzle or turbine nozzle assembly capable of accommodating the relative thermal movement between the turbine nozzle and the GTE-turbine nozzle mounting interface during GTE operation. Preferably, embodiments of such a turbine nozzle assembly would be relatively compact while providing a mounting flange sealing surface sufficiently thermally isolated from the combustive gas flow to prevent overheating of any compression seals disposed between the mounting flange and the GTE-turbine nozzle mounting interface. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying Drawings and this Background.